1. Field of the Invention
The present invention relates to a technology for displaying an input image signal at a frame rate higher than an original frame rate.
2. Description of the Related Art
Conventionally, there has been a method in which a frame rate of an inputted image signal is doubled, and a motion blur and a flicker are reduced by alternately outputting a sub-frame in which a spatial high-frequency component is emphasized and a sub-frame in which the spatial high-frequency component is suppressed (for example, Japanese Patent Application Laid-open No. 2006-184896).
However, the conventional art described above has had a problem that that the effect of improving video resolution is reduced when an image signal level exceeds the maximum gradation by the emphasis of the spatial high-frequency component. For example, an 8-bit image signal takes 256 step levels of 0 to 255 (gradation values). When the spatial high-frequency component is emphasized in such image signal, in a pixel which originally has high gradation, the image signal level after the emphasis may exceed 255 as the maximum gradation. Since the image signal exceeding the maximum gradation can not be displayed on a display panel, a portion exceeding 255 has been cut off by using a clip circuit or a limiter circuit and the maximum level of the image signal has been limited to 255 or less. However, by this operation, apart of the high-frequency component of the image signal is lost, and particularly in a high gradation range, the effect of improving video resolution is reduced.